Biliary inter-relationship between phospholipid, bilirubin and taurocholate in the anaesthetized rat

The interference between biliary phospholipid and bilirubin secretion was investigated in rats with bile fistulae, under conditions of normal and maximal bilirubin secretion. The enterohepatic circulation of bile salts was interrupted and the animals received infusions of sodium taurocholate, a micelle-forming physiological bile salt. Sodium taurocholate infusion (0.19 mumol min-1 100 g-1 body weight) induced an increase in bile flow and phospholipid secretion, while basal bilirubin secretion was not increased. Bilirubin infusion (0.26 mumol min-1 100 g-1 body weight) induced a decrease in basal and taurocholate-stimulated phospholipid secretion. Biliary mixed micelle formation was presumably altered during bilirubin infusion, although bile taurocholate concentration, taurocholate secretion rate and bile flow were not modified. When sodium taurocholate was infused during bilirubin-decreased phospholipid secretion, this secretion was restored but maximal biliary bilirubin secretion was not increased. These results provide circumstantial evidence for the hypothesis that mixed micelle formation is not an important determinant of maximal bilirubin transport into bile.